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Optical element and optical pickup apparatus

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Title: Optical element and optical pickup apparatus.
Abstract: A production method of an objective lens for optical pickup apparatus having a numerical aperture NA of image side of 0.80 to 0.90 is disclosed. The method includes steps of molding resin composition containing copolymer of α-olefin and a cyclic olefin represented by Formula (I) or (II) to form lens shape, and thermally processing the molded product under a condition at a temperature between Tg −45° C. and Tg −15° C. for 12 to 168 hours, wherein the Formula (I) and (II) is detailed in the specification. ...


USPTO Applicaton #: #20090312510 - Class: 526281 (USPTO) - 12/17/09 - Class 526 


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The Patent Description & Claims data below is from USPTO Patent Application 20090312510, Optical element and optical pickup apparatus.

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This application is based on Japanese Patent Application Nos. 2008-155046 filed on Jun. 13, 2008 and 2008-192241 filed on Jul. 25, 2008 in Japanese Patent Office, the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a production method of an objective lens used for an optical pickup apparatus, an objective lens used for an optical pickup apparatus and an optical pickup apparatus.

BACKGROUND

Apparatus reading and recording information such as players, recorders and drives for an optical information recording media, for example, MO, CD, or DVD, include an optical pick up device. The optical pick up devices have an optical unit which exposes light having predetermined wavelength to the medium and accepts the reflected light by a detecting element, and the optical units have an optical element such as an objective lens which condensing the light flux at a reflective layer of the recording media or accepting elements. Plastic materials are suitably used for the optical elements of the optical pickup lens in view of low cost production by such as injection molding. Copolymers composed of cyclic olefin and α-cyclic olefin are known for the suitably applicable the optical element. (For example, Patent Document 1)

Blu-Ray Disc (“BD”) recording apparatus or media recording or reproducing information employs an objective lens having a numerical aperture NA of image side of 0.80 to 0.90, representatively 0.85, and light source having wave length of 380 to 420 nm (usually 405 nm) have been developed which can record information with higher density than CD (NA: 0.45, wavelength: 780 nm) or DVD (NA: 0.65, wavelength: 635 or 650 nm).

Patent Document 1: JP A 2002-105131

A spot beam can be made small in the optical pickup apparatus for BD use shorter wave length and having larger NA than the optical pickup lens for conventional CD or DVD, and realize high recording density. On the other point of view, high sensitivity and strict optical performance are required. Light stability different from the conventional optical pickup lens is required adapted for shorter wave length of light source, and higher level of stability performance used at high temperature is required, and therefore, it is not responsible to proper stability against light or heat of the resin material. Very high accuracy as well as high stability are required because it is exposed to strict temperature condition due to heat of driving device such as tracking in addition to high stability against light, particularly for an objective lens which condense the light flux to the recording media. The inventors have found that the deterioration of lens performance is caused by stress relaxation at high temperature and resin deterioration due to blue laser of wavelength of 280 to 420 nm in complex as a result of study for stability performance against light and durability performance.

In view of foregoing, an object of the present invention is to provide a production method of an objective lens used for an optical pickup apparatus, an objective lens used for an optical pickup apparatus and an optical pickup apparatus in which the durability and deterioration of aberration are improved.

SUMMARY

OF THE INVENTION

A production method of an objective lens for optical pickup apparatus having numerical aperture NA of image side of 0.80 to 0.90, comprises steps of molding resin composition containing copolymer of α-olefin and a cyclic olefin represented by Formula (I) or (II) to form lens shape, and thermally processing the molded product under a condition at a temperature between Tg −45° C. and Tg −15° C. for 12 to 168 hours.

In the formula, n is 0 or 1, m is 0 or a positive integer, and k is 0 or 1. In the case where k is 1, the ring that is shown using k has 6 member rings, while the ring has 5 member rings when k is 0.

R1 to R18 and Ra and Rb independently represent a hydrogen atom, a halogen atom or a hydrocarbon group. The halogen atom herein represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.

In the formula (II), p and q independently represent 0 or a positive integer and r and s independently represent 0, 1 or 2. R21 to R39 independently represent a hydrogen atom, a halogen atom, a hydrocarbon group or an alkoxy group.

An objective lens produced by a method of this invention can be free from composition causing deterioration due to heat and have improved stability against light due to blue laser radiation by processing under a condition at a temperature between Tg −45° C. and Tg −15° C. for 12 to 168 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic structure of the optical pickup apparatus.

DETAILED DESCRIPTION

OF THE PREFERRED EMBODIMENT

The preferred embodiment according to the present invention is described in detail.

The objective lens has numerical aperture NA of image side of 0.85, and is composed of a copolymer of α-olefin and a cyclic olefin represented by Formula (I) or (II). The lens is subjected to thermally processing under a condition at a temperature between Tg −45° C. and Tg −15° C. for 12 to 168 hours. The condition is determined to maintain aberration variation of 0.01 rms λ or less, required for good characteristics for the objective lens.

Composition material of the objective lens is described.

The composition material of the objective lens includes a copolymer of α-olefin and a cyclic olefin represented by Formula (I) or (II)

The cyclical olefin is preferably represented by the following general formula (I) or (II).

In the formula, n is 0 or 1, m is 0 or a positive integer, and k is 0 or 1. In the case where k is 1, the ring that is shown using k has 6 member rings, while the ring has 5 member rings when k is 0.

R1 to R18 and Ra and Rb independently represent a hydrogen atom, a halogen atom or a hydrocarbon group. The halogen atom herein represents a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.

Examples of the hydrocarbon group include an alkyl group having 1-20 carbon atoms, a halogenated alkyl group having 1-20 carbon atoms, a cycloalkyl group or an aromatic hydrocarbon group having 3-15 carbon atoms. More specifically, examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an amyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group and an octadecyl group. These alkyl groups may be substituted by a halogen atom.

An example of the cycloalkyl group is cyclohexyl. Examples of the aromatic hydrocarbon include a phenyl group, a naphthyl group. In addition in the general formula (I), R15 and R16, R17 and R18, R15 and R17, R16 and R18, R15 and R18 or R16 and R17, may each bond (with each other) and form a monocyclic or polycyclic group, and the monocyclic or polycyclic group formed in this manner may have double bonds. Specific examples of the monocyclic or polycyclic group formed herein are given below.

The carbon atoms that have been numbered 1 or 2 in the above example represent carbon atoms that bond with R15 (R16) or R17 (R18) respectively of the general formula (I).

Also an alkylidene group may also be formed with R15 and R16 or R17 and R18. This type of alkylidene group has 2-20 carbon atoms and specific examples of this type of alkylidene group include an ethylidene group, a propylidene group and an isopropylidene group.

In the formula (II), p and q independently represent 0 or a positive integer and r and s independently represent 0, 1 or 2. R21 to R39 independently represent a hydrogen atom, a halogen atom, a hydrocarbon group or an alkoxy group.

The halogen atom herein is the same as the halogen atom in general formula (I). Examples of the hydrocarbon include an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aromatic hydrocarbon having 3-15 carbon atoms. More specifically, examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an amyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group and an octadecyl group. These alkyl groups may be substituted by a halogen atom.

An example of the cycloalkyl group is a cyclohexyl group. Examples of the aromatic hydrocarbon include an aryl group and an aralkyl group, and more specifically, a phenyl group, a tolyl group, a naphthyl group, a benzyl group and a phenylethyl group.



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stats Patent Info
Application #
US 20090312510 A1
Publish Date
12/17/2009
Document #
12482037
File Date
06/10/2009
USPTO Class
526281
Other USPTO Classes
264/26, 359355
International Class
/
Drawings
2


Numeric
Numerical Aperture
Objective Lens
Pickup


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